Generally used air-conditioning apparatuses having a multi-room heat-pump refrigeration cycle circuit include an outdoor unit including a compressor, a four-way valve, and an outdoor heat exchanger, and a plurality of indoor units each including an expansion valve and an indoor heat exchanger. These components sequentially communicate with one another through refrigerant pipes, and form a heat-pump refrigeration cycle. Specifically, the indoor units have a parallel configuration, and form a predetermined refrigeration cycle circuit by switching between a cooling operation and a heating operation.
Such multi-room air-conditioning apparatuses adjust a flow rate of the refrigerant in the entire refrigeration cycle circuit by adjusting an operation capacity of the compressor using a condensing temperature of the indoor heat exchangers as a target value in the case of the heating operation. Also, each of the indoor units adjusts a flow rate of the refrigerant in the indoor heat exchanger by adjusting an opening degree of the expansion valve using a degree of subcooling of the indoor heat exchanger as a target value. That is, a capacity of the indoor heat exchanger is designed such that a predetermined heating performance is achieved for a load of the indoor unit by adjusting a condensing pressure and a degree of subcooling within predetermined ranges in the case of the heating operation. In the case of the cooling operation, an evaporating pressure and a degree of superheat are adjusted within ranges determined in a predetermined extent.
In addition, as for air-conditioning apparatuses including a plurality of indoor units installed in the same room, there has been proposed an air-conditioning apparatus that performs an air-conditioning performance saving operation in any of the indoor units in the case where a detected air-conditioning load of a refrigerant circuit is larger than a heating performance rating preset for the refrigerant circuit (see, for example, Patent Literature 1). This air-conditioning apparatus determines whether a capacity of a compressor has reached the maximum capacity during the heating operation. Upon determining that the capacity of the compressor has reached the maximum value, the air-conditioning apparatus determines whether the performance of the entire system is sufficient or not for a heating load on the basis of a value obtained by subtracting a calculated high-pressure saturation temperature from a high-pressure saturation temperature target value. If the performance of the entire system seems to be insufficient, the air-conditioning apparatus changes a set degree-of-subcooling target value to a larger value in the order of ascending priority to perform a heating performance saving operation. In the case of the cooling operation, a set degree-of-superheat target value is changed to a larger value.
Also, as an air-conditioning apparatus capable of performing a simultaneous cooling and heating operation, there has been proposed an air-conditioning apparatus in which a water temperature adjusting unit capable of heating water used is connected to an air-conditioning heat source unit in parallel with indoor units (see, for example, Patent Literature 2). In the case of simultaneously performing heating and a water heating operation, this air-conditioning apparatus determines that air-conditioning-side performance is insufficient when detecting that a high pressure has become a pressure lower than a preset certain pressure. The air-conditioning apparatus performs control for prioritizing indoor air-conditioning by reducing an opening degree of a water use side refrigerant flow control device to a predetermined minimum opening degree. Also, when detecting a high pressure higher than the predetermined pressure, the air-conditioning apparatus enables a water heating operation to be performed at the same time as indoor air-conditioning by increasing the opening degree of the water use side refrigerant flow control device to a predetermined opening degree.